On messing with perfection

Q: What is Andrés Muñoz's current ERA and how does it compare to last season?

Andrés Muñoz currently has a 6.00 ERA, which is significantly higher than his performance last season.

Q: How many home runs has Muñoz allowed this season compared to last?

Muñoz has allowed three home runs this season, which is more than the two he allowed all of last season.

Q: What are the key statistics indicating Muñoz's struggles this season?

Muñoz has experienced five 'meltdowns' and has a 50% hard hit rate against him, alongside a .533 xwOBAcon ranking near the bottom among pitchers.

Q: What changes have been observed in Muñoz's pitching style this season?

Muñoz's four-seamer and sinker have less arm-side run and decreased spin efficiency in 2026, affecting his overall performance.

SEATTLE, WASHINGTON - MAY 05: Andres Munoz #75 of the Seattle Mariners reacts while taking the mound during the ninth inning against the Atlanta Braves at T-Mobile Park on May 05, 2026 in Seattle, Washington. (Photo by Jack Compton/Getty Images) | Getty Images Andrés Muñoz changed for some reason. It’s been a rough early going for the Mariners’ star closer. Muñoz has a 6.00 ERA and has already allowed more home runs (three) than he did all of last season (two). He’s been pinned with five “meltdowns,” or outings where his WPA was less than to -0.06 — basically, a more comprehensive version of blown saves. Batters have a 50% hard hit rate against him and a .533 xwOBAcon, which ranks next to last among pitchers with at least 15 innings pitched. Despite all the hard contact, Muñoz is still getting tons of whiffs and strikeouts. His 42.7% whiff rate is the best in baseball — except for Mason Miller’s anti-human 57.8% — and his 37.9% strikeout rate is top five. We can see he occupies a unique space on the whiff versus quality of contact chart:

I’m going to start by saying Muñoz is probably fine. He has a stretch like this at least once a season, where batters hit him hard. Mixed with an always-high walk rate, that turns into lots of runs. Muñoz may very well go down as by the time he reaches free agency after 2028, but he is still a reliever, prone to the violent swings of one-inning samples. Still, by xwOBA allowed, we’re witnessing the worst stretch of his career: How? Why? I don’t know, is the truest thing I can say. While I’m going to do my best to step through the data, the thing I’m most confident in telling you is that there isn’t a one-size-fits-all, universal truth to pitching — pitchers can be good and bad despite all sorts of peripherals. Let’s start with a plot from Baseball Savant, showing Muñoz’s horizontal movement by year: Muñoz four-seamer and sinker have much less arm-side run in 2026, with the four-seamer specifically moving three inches less than it did last year. His is also down about seven points, suggesting he’s releasing the baseball a bit different in 2026. Stuff+ thinks this version of Muñoz’s four-seamer, with less movement and different spin, is much worse, though the profile doesn’t look far removed overall: Muñoz has always had something of a weird fastball. It’s on the flatter end of the spectrum, meaning it enters the zone on a line, rather than if he were pitching from the top of a 10-foot ladder. Flat fastballs are often associated with more whiffs — think and — whereas steep fastballs are often associated with more grounders. Despite its flatness, however, Muñoz’s fastball has been more of a ground ball pitch. Why? That gets us to the concept of the “dead zone.” The term is used to describe fastballs that — based on their spin, angle and other physical properties — tend to move predictably and perform poorly. A good fastball isn’t always about getting lots of movement, but lots of movement relative to what a batter might infer out of hand. Before joining the in 2025, Max Bay . Here we can see that Mason Miller often imparts vertical movement on his fastball that batters simply wouldn’t expect, helping explain why they so often swing (and miss) under the pitch: And here we can see Muñoz, with significant overlap on his expected and actual movement. This suggests batters are more likely to swing accurately at the pitch, perhaps explaining why they posted a 59% hard hit rate on it last year: But Bay’s “dead zone” calculation intentionally doesn’t incorporate velocity as a variable (for a variety of good reasons). Alex Chamberlain wrote a great piece about this “” last year for FanGraphs, specifically discussing Muñoz’s fastball. When factoring Muñoz’s big velocity, Chamberlain noted batters should infer more “rise” on the pitch than implied by the dead zone, convincing them to swing too high and beat it into the ground. That’s likely why a four-seamer would normally get blown up could still serve as a (moderately) useful tandem for his other-worldly slider. Looking at the dead-zone metrics this year (), it’s possible this dynamic has changed: I’m reluctant to make any sort of broad judgements about these figures, but it certainly looks like Muñoz is even closer to the dead zone than before, especially horizontally. And if his fastball had previously rested on a delicate balance of traits, it’s possible these changes have eliminated the grounder-inducing properties, allowing batters to elevate their hard contact. That’s not good. So, why make this change? I should say up front that I don’t know if this intentional. I’m far from an expert on these figures, and I don’t know how much they fluctuate in season. This could very well be a mechanical blip, or even just “how it goes.” If it is intentional, however, I can only guess at the thinking. Again, Muñoz’s fastball last year wasn’t good for much more than stealing strikes and creating hard grounders, so a tweak was justified. The fastball also appears to be with his slider, and the new shape gives him a greater range of total movement, making him less predictable in aggregate. His total whiff rate jumped from 36.5% to 42.7% this year. I also haven’t addressed the corresponding changes to his sinker. Maybe whatever tweak we’re seeing in his four-seamer is causing the extra inch of drop on his sinker, allowing him to, you know, not throw it right down the middle all the time. The stuff and location models love this change. Like, if you already have a dead-zone fastball that you’re using as a sinker, maybe it’s best to simply improve the sinker. It’s a pitch he mostly throws to righties, and it’s swapped places this year with his four-seamer as the get-me-over pitch when behind in counts. Muñoz has a 0.00 FIP and 51% strikeout rate against righties this year. There is *something* about the profile that is working. But Muñoz was already great against both handedness, and now he’s struggling to get the four-seamer past lefties. The Mariners and their pitchers are known for endless tinkering, and the returns have been somewhat mixed, with equal-and-opposite reactions to create offsetting gains (think and ). Obviously, the have been outstanding, but that’s only because Hancock wasn’t doing anything well before — the only direction he could go was up. There wasn’t much more for Muñoz to reach for. Now there is. Regardless of these changes and impacts (and the reasons behind them), it’s probably not too big of a deal. I’m overall confident in any pitcher getting so many whiffs, and I expect those to win out over time. I do think this iteration of Muñoz’s fastball will continue to get hit hard, and I expect less of that contact will come on the ground. But really the biggest issue in his early line is not the shape of his fastball but a few middle-middle mistakes. There’s hardly a pitch that can survive poor locations. The final thing I will say is probably the only thing I should have said: Relievers.